Process for the manufacture of chromium compounds



Patented June 7, 1927.

PAUL wmsn, or wmsnoar, NEAR ooLoen -oN-rnE-anmn GERMANY, ASSIGNOR Eve I.G. FARBENINDUSTRIE AKTIENGESELLSGHAFT, OF FRANKFORT-ON-THE-HAIN GERMANY-PROCESS FOR THE MANUFACTURE OF CHROMIUM COMPOUNDS.

'No Drawing. Application flied March 6, 1926, Seria111'o. 92,837, and inGermany August 24, 1925.

The processes for the manufacture of chromium compounds from chrome oreemplo ed in industry up to the present time sufl er fromthe disadvantagethat the in:

volve losses of ore which are very di cult to recover. According to mostof such processes a diluent is added to the mixture ofchrome ore andalkali, as for example chalk, dolomite, iron oxide, etc., thesesubstances being only recoverable in exceptional cases. In most casesthey are completely lost with the unattacked ore, thus causing avconsiderable increase in the cost of the process. Proposals have alreadybeen made for usingas diluents such materials as can be recovered in aform available for further use. Thus the German Patent No. 166,767suggests the 'use of finely crushedv chrome ore but theprocess accordingto this patent is restricted to the joint use of ahand fed furnace. Inorder to obtain a satisfactory attack, when working with mechanicalfurnaces and with ;mixtures of finely crushed. chrome ore and alkalimetal carbonates or hydroxides, very large amounts 'of ore in proportionto the material used for attacking the ore must be emplo ved, as forexample six times the quantity o finely crushed ore. This is due to thefact that a certain amount. of diluent material must be present in orderto render the melt sutficiently porous that the air-oxygen required tobring about the attack can pene trate into the interior of the chargeand of the clinker produced.

According to the present invention satisfactory working can be achieved\with a much smaller quantity of ore acting as the diluent material andto prevent caking if ore of a definite grain size is employed. In thismanner only the most finely crushed portions of the'ore arepreponderantly attacked while the coarser portions remain practicallyunaltered and serve as diluent material thus preventin the otherwiseunavoidable caking togeter of the charge. The application of myinvention increases the pro uctive capacity of the wliole. process Iconcerned.

The method of working is as follows The moist or dr mixture of an orewhich leaves a residue of 1530% on a sieve of 70 mesh per cm. with somuch of the 'decomposition agent that the content of the same amounts to28 32% are heated in an oxidizing atmosphere to the reaction temperatureof over 1100 C. The sintered melt is leached with Water, advantageouslyin the presence of a small amount of acid in order to decompose thealuminate. The chromate which then passes into' solution is separatedfrom the residue and 'worked up in the customary manner.

-The residue after the leaching operation consists of unattacked chromeore; alumina, magnesium and iron oxide. For the recovery of theunattacked chrome ore mechanical methods may be employed, as for examplesedimentation or sorting processes.

However it has been discovered that the most advantageous means is notthe mechanical but the chemicaLmethod, according -to which it ispossible by treatment of the residue with dilute acid to recover achrome ore almost completelyfree from admixed substances. It isessential in this connection,

however, that the concentration of the acid should'not be too hi h,as'otherwise the final liquors obtained are iflicult to filter.Particularlyfavourable are acids of about B. Sulfuric acid of from 5 B.to 30 B. may be used. It is likewise advantageous to moderately heat theacid although it is advisable not to allow the temperature to rise aboveC. In general temperatures ranging from atmospheric temperature, 15C.,up.to

60 C. may be employed. If these conditions are taken into account aresidue is obtained which can ,be filtered ofi quite easily.

, The amourit of acid employed may vary Within wide limits, either thetheoretical amount, an insuflicient amount, or an excess, may beemployed. C I

. When using the theoretical quantity of acid the final liquors obtainedare diflicult to filter and this method is therefore only selected inspecial cases.

I When an insuiiicient quantity of acid is" employed the recoveredchrome ore still contains corresponding quantities of iron and magnesiumoxide s. A proportionate quantity of acidmay be added in order tomaintain the content of these impurities the same or by varying the acidthe amounts of the impurities may be allowed to increase. In the lattercase the possibility arises that the ,melt may become so enriched iniron and magnesium oxides that the decomposition agents added to thecharge'may just succeed in, attacking the whole of the available chromeore. The resulting, residue is then practically free from chromium andmay be thrown away.

By the application of an excess of acid pure ore is invariablyrecovered.

When using either an insuflicient quantity of acid or an excess of acidthe liquors obtained can be filtered with ease. The velocity of reactionis very great in all cases.

Therecovered ore, with or without the addition of fresh ore, is broughtto the desired grain size by means of suitable appli times and returnedto the charge.

The following examples will serve to illustrate my invention:-

Ewa mple parts of ground chrome ore of any composition and leaving aresidue of 25% on a sieve'of 70 mesh per cm. are'intimately mixed with30 parts of sodium carbonate. According to the construction of therevolving furnace and the feeding arrangement, .the mixture may beintroduced into the furnace either moist or dry and there heated in thecustomary manner to.

above 1100 C.- The resultin melt is quenched in water, allowed to soakand the chromium liquor leached and separated from the water-insolubleportion. For the purpose of recovering the unattached chrome ore thiswater-insoluble portion is treated with so much sulphuric acid of 15 B.at 50 C. that not all the iron and magnesium oxides are dissolved; theweakly basic liquor is separated off and the residue dried. This residueis mixed with a fresh supply ofore of the required grain size and withsodium carbonate and returned to the furnace. The amount of sulphuricacid required as the process proceeds should be always adjusted so thatthe basicity ,of the liquor remains always the same. The yield ofchromate obtainedis about 90% calculated on the amount of-sodiumcarbonate used.

.Ewample. 2.The Water-insoluble portion as obtained in example 1,'afterthe separation of the chromate liquor is treated with suflicientsulphuric acid of about 20 B. in the cold that after the dissolution ofall the undesirable impurities a slightly acid solucial heating. Therecovered ore can be em-i ployed in a fresh charge without furthertreatment.

Example 3.-The water-insoluble portion obtained according to Example 1,is treated with sulphuric acid according to the counter-currentprinciple. Thereby the almost extracted ore comes into contact withfresh acid, and thus the acid may be selected of any desired strength.As the process of extraction proceeds further, the most suitabledilution can be easily adjusted by the addition of water.

Iclaim: 1. In processes for the manufacture of chromium compoundsinvolving the use of mechanical furnaces, the steps which consistessentially in forming a mixture of an alkali with chrome ore of such agrain size that a residue of from 15% to 30% remains on a sieve of 70mesh per 0. m., heating the mixture to a reacting temperature above 1100C., leaching the furnaccd mixture, treating the undissolved residue ofthe leaching step with acid, and using the residue of the acid treatmentwith fresh chrome ore as the starting material in a subsequentoperation.

2. Process for the manufacture of chromium compounds as defined in claim1, in which dilute acid is used for treating the undissolved residue ofthe leaching step, and the residue of the acid treatment is separatedfrom the dilute acid by filtering at the temperature of the greatestfiltering velocity.

3. Process for the manufacture of chromium compounds as defined in claim1, in which a quantity of acid insufiicient to dissolve the impuritiespresent in the undissolved residue of the leaching step is employed intreating said undissolved residue.

1L Process for the manufacture of chromium compounds as defined in claim1, in which sulfuric acid of from 5 to 30 B. is used in treating, theundissolved residue of the leaching step and the acid treatment iscarried out at a temperature of from about, atmospheric temperature tonot exceeding 60"? i In testimony whereof I have hereunto set my hand. 1

PAUL WEISE.

